Heretofore, a variety of limitations have affected the molding of threaded plastic components. When a hydraulically powered rack was employed for extracting a metal core from a mold cavity, the number of threads which could be made on the inside or the outside of a component was limited because the number of threads was restricted by the number of rotations required for unscrewing the metal core from the component. The number of rotations which a core could make was dependent upon the space required around the mold to accommodate the length of the rack. Moreover, hydraulically powered equipment had problems of fluid spills and fluid leakage. Keeping an adequate supply of hydraulic fluid on hand was a limitation as well. In addition, halting a hydraulically driven rack's travel precisely was difficult to achieve, and the result was that substantial tolerances in the finished components were required. Also, because substantial mechanical movement was required for the rack, the speed of ejecting finished components was restricted.
Electric motors have been used in molding machine applications also. For example, U.S. Pat. No. 3,737,268, FIG. 12, illustrates the use of an electric motor for driving a shaft connected to a metal core with a threaded end inside a molded plastic component in order to turn and loosen the core and free it. In that patent, the core is moved rotationally by a belt-driven motor. A pair of ejector rods, powered by a second motor timed to cooperate with the first, are linearly moved to push the loosened component off the core.
Another patent illustrating the use of a pair of electric motors is U.S. Pat. No. 5,110,522. This patent relates particularly to an injection molding machine in which two motors are required for handling certain rectilinear and rotative drive requirements. Similarly, two motors are required for the rectilinear and rotative drives identified in U.S. Pat. Nos. 5,792,483 and 5,911,924.
U.S. Pat. No. 6,051,896 is an example of a patent which discloses the use of servo controlled electric motors in a molding machine. In that patent, one of the motors controls linear motion, and a second motor controls rotary motion. U.S. Pat. No. 6,142,760 is generally similar, as is U.S. Pat. No. 6,267,580.